The cost of a private beach starts at €25 (Opera beach) for a lounge chair and umbrella and runs to €65 per person N La Plage.
Since it is forbidden to bring your own food to a private beach, add in the cost of a meal. Prices vary widely. A main course at a private beach-restaurant starts at around €21 for a pizza, pasta or large salad and runs to €30 or €40 for a grilled fish.
The cheapest place for a lounge chair/parasol rental is Opera beach. For a meal, Blue Beach and Hotel Amour beach restaurants are the most budget-conscious.
At first glance, it's easy and obvious to say that going to a free public beach is cheaper than laying out money for a managed private beach. If you live on the Cote d'Azur that's certainly true because you already have a beach towel, mat, umbrella, shoes and plenty of other equipment to make your day at the beach comfortable. When you come as a visitor however, your beach experience can require a substantial cash outlay. Hotels do not provide beach towels or beach umbrellas. Beach towels alone cost €6 or €7 at a private beach club.
To be truly comfortable on a public beach, you would want a rubber or bamboo mat under your beach towel. Count on at least €12. Obviously, that can't compare to a lounge chair topped with a mattress. To get from the water to your towel, you'll at least need a pair of flip-flops (€5) but even better are rubber water shoes (€10). On a private beach, bambou mats run down to the water's edge, making the extra footware unnecessary.
And what about food and drink? You can picnic on a public beach for much less than a beach-restaurant. The pan bagnat sandwich that you can buy for €6 in a sandwich shop costs €20 in a beach restaurant and that's usually the cheapest item on the menu. You do not save money however, by ordering a meal in a cafe/restaurant along the Promenade des Anglais as their prices are roughly the same as their counterparts on the beach.
The bottom line? For just a day at the beach as part of a visit-the-French Riviera experience, it's more comfortable and not much more expensive to spend the day at a private beach. If you'll be hanging at the beach for two or more days, invest in the proper acoutrements and you'll have a fine time at a public beach.
Note that the prices below are for early summer and are correct at the time of publication. Some beaches may raise prices from mid-July to mid-August. Off-season you can usually get a few euros shaved off. In most cases the half-day price is only for the afternoon after 2 or 3pm. Hotel Amour plage is one of the few to offer a half-day price from 9am to noon. In most places you'll pay more to relax in the front row with an unimpeded sea view.